THIN-FILM HETROJUNCTION BY CARBON NANOTUBE DERIVATIVES WITH ENHANCED SOLUBILITY AND OPTICAL PROPERTIES

The combination of single-walled carbon nanotubes(SWNTs), characterized by high electron mobility, with p-typesemiconducting polymers could lead to an overall improvementin the exciton dissociation and carrier extraction efficiencies inpractical devices.1However, one of the main concern in the use ofSWNTs, relates to the their scarce solubility. Chemicalmodification has been widely employed to increase the solubilityof SWNTs, but usual reaction conditions limit such syntheses toa small scale with low productivity.Here, we employ SWNTs which have been functionalizedwith aromatic and heteroaromatic moieties via 1,3-dipolarcycloaddition and through diazotization reaction under batch andcontinuous-flow conditions. This offers a safer, scalableprocessing and the opportunity to a rapid reaction screening usinga relatively small amount of reagents.2Such systems in combination with P3HT have been used tofabricate bulk heterojunctions (BHJ) by Langmuir-Blodgett,which offers a simple method of producing ultrathin-films withfine control over thickness. Thanks to the improved solubility ofSWNT derivatives we prepared multi-planar heterojunctions(MHJ) consisting of alternate layers of P3HT and SWCNTs, byhorizontal lifting (Langmuir-Schaefer) technique. Then weinduced a transition from MHJ to BHJ by thermal annealing tomix the layers.While the degree of functionalization ensured bydiazotization, higher than 1,3-dipolar cycloaddition, improvesprocessability, fluorescence quenching measurements havedemonstrated that thienyl groups ensure a stronger interactionwith P3HT and consequently a better electron transfer. Suchproperties have been modulated within the thin film by changingits internal morphology tuning the parameters of the mixingprocess. Thienyl derivatives obtained through controllablefunctionalization of SWNTs in flow conditions are promisingcandidates for the incorporation in the active layer of OPV cells.